1. Field of the Invention
The present invention relates to semiconductor devices with a fuse forming a redundancy circuit for repairing a defective product and a manufacturing method thereof.
2. Description of the Background Art
FIG. 8 shows an exemplary structure of a semiconductor device with three interconnection layers and a fuse. In this semiconductor device, on a surface of a silicon substrate 1 serving as a semiconductor substrate, a field oxide film 10 is selectively formed as an isolating insulating film. Further, a fuse 11 is selectively formed from polycrystalline silicon so as to contact with an upper side of field oxide film 10. Fuse 11 is an element constituting a redundancy circuit for repairing a defective. Through the blow of fuse 11 by a laser, a defective portion can be disconnected and a normal portion can be employed instead, if necessary.
When fuse 11 of polycrystalline silicon is to be formed on a semiconductor device, which is a so-called xe2x80x9cthree-layer productxe2x80x9d, having three interconnection layers on a semiconductor substrate with an insulating layer interposed between each interconnection layer and its adjacent layer, total thickness of three oxide films 21a, 21b, 21c serving as insulating layers for mutually isolating interconnection layers 23a, 23b, 23c exceeds 20,000 xc3x85. Therefore, when the blow of the fuse is necessary to repair a defective product, for example, a significantly high output of the laser is required for blowing the fuse. When the output of the laser is extremely high, however, the radiation of laser causes a crack in the field oxide film under the fuse and the blown fuse directly contacts with silicon substrate 1 whereby a minute current flows.
To solve the problem described above, the oxide film can be thinned in a region above the fuse as shown in FIG. 9. Such structure is described in Japanese Patent Laying-Open No. 9-51038, for example. With such structure, the fuse can be securely blown by the laser with an output of the same level both in the three-layer product and a product with one layer of an oxide film. At the same time, as the fuse blow is possible with a low laser output, undesirable effect such as crack of the field oxide film can be prevented.
Next, a process for obtaining the structure shown in FIG. 9 will be described.
First, a structure shown in FIG. 10 is formed. In particular, a field oxide film 10 with a thickness of about 5000 xc3x85 is formed on a silicon substrate 1, and a fuse 11 of polycrystalline silicon is formed on field oxide film 10. Then, an oxide film 21a with a thickness of about 8000 xc3x85 is formed so as to cover fuse 11. A vertical interconnection 22a electrically connecting a contact 13 with an upper part is provided to form a first interconnection layer 23a. Then an oxide film 21b with a thickness of about 12,000 xc3x85 is formed so as to cover an upper side of first interconnection layer 23a. Then, a vertical interconnection 22b electrically connecting first interconnection layer 23a with an upper part is provided to form a second interconnection layer 23b. Further, a vertical interconnection 22c electrically connecting second interconnection layer 23b with an upper part is provided to form a third interconnection layer 23c. Thus the structure shown in FIG. 10 is obtained.
With reference to FIG. 11 a photolithography is performed to form a resist mask 14 for removing oxide film 21c in a region including a region 26 (hereinafter referred to as xe2x80x9cfuse regionxe2x80x9d) above fuse 11 by the etching. Here, resist mask 14 is formed with an opening slightly wider than fuse region 26 therein to accommodate the decrease in the opening area in a subsequent step caused by the formation of a glass coat 12 (see FIG. 9) with a thickness.
With reference to FIG. 12, oxide film 21c with the thickness of about 8000 xc3x85 is removed by the wet etching and dry etching using resist mask 14. After the removal of resist mask 14, glass coat 12 is deposited through CVD (Chemical Vapor Deposition). Further, a mask (not shown) is formed on glass coat 12 for the formation of the opening in glass coat 12. Then the photolithography and etching are performed so as to form fuse region 26 with a predetermined opening pattern. Then with the removal of the material of mask, the structure shown in FIG. 9 is eventually obtained.
When the structure as shown in FIG. 9 as described above is to be obtained, in order to form an opening in fuse region 26, an additional mask must be formed after the formation of glass coat 12, and then the photolithography and the etching must be formed. Thus the number of the required process steps increases. In addition, an additional amount of the mask material is necessary.
Therefore, an object of the present invention is to provide a semiconductor device and a manufacturing method thereof allowing the reduction in the number of process steps and the amount of necessary mask material.
To solve the problems described above, a method of manufacturing a semiconductor device according to the present invention includes the steps of: forming a fuse in contact with an upper surface of the isolating insulating film formed on a main surface of a semiconductor substrate; forming a lower insulating layer on the semiconductor substrate and selectively forming a lower interconnection layer in contact with an upper surface of the lower insulating layer; selectively forming an upper insulating layer in contact with upper surfaces of the lower insulating layer and the lower interconnection layer, and covering a region except an uppermost vertical interconnection region viewed from above including a vertical interconnection for electrically connecting the lower interconnection layer and another interconnection layer above and an internal region of the uppermost vertical interconnection region; and selectively forming an upper conductive layer in contact with exposed upper surfaces of the lower insulating layer, the lower interconnection layer and the upper insulating layer in a region outside a fuse region covering a plane region including the fuse and a neighborhood thereof
With the above-described method, in the step of selectively forming the upper insulating layer, the upper insulating layer is formed in the form having the opening for the vertical interconnection to be formed in the upper insulating. In addition, the vertical interconnection for electrically connecting interconnection layers placed above and below the upper insulating layer and the interconnection layer to be placed on the upper side of the upper insulating layer are formed together as one conductive layer. Thus the number of process steps can be reduced.
In one embodiment of the above-mentioned invention, the step of selectively forming an upper conductive layer includes the steps of: forming the upper insulating layer in contact with upper surfaces of the lower insulating layer and the lower interconnection layer; and removing the upper insulating layer in the uppermost vertical interconnection region and the internal region.
With the above-described method, in the step of selectively forming the upper insulating layer, the upper insulating layer is removed not only in the region corresponding to the opening for the vertical interconnection to be formed in the upper insulating layer but also in the fuse region. Thus the number of process steps can be reduced. Along with the reduction in the number of process steps, the necessary amount of mask material can be reduced as the number of etching processes can be reduced.
In the above-mentioned invention, the step of selectively forming an upper conductive layer preferably includes a step of forming the upper conductive layer outside of the fuse region at a distance not shorter than the thickness of the coating intended to be formed on the upper conductive layer from an outline of the fuse region.
With the above-described method, the fuse region can certainly be maintained in an opening state even if a coating is performed on the upper conductive layer in a later step.
Further, to solve the problems described above, a semiconductor device according to the present invention includes: a semiconductor substrate; an isolating insulating film formed on a main surface of the semiconductor substrate; a fuse formed in contact with an upper surface of the isolating insulating film; a lower insulating layer and a lower interconnection layer selectively formed to be in contact with an upper surface of lower insulating layer on the semiconductor substrate; an upper insulating layer selectively formed to be in contact with upper surfaces of the lower insulating layer and the lower interconnection layer; the upper insulating layer being placed only in a region outside the uppermost vertical interconnection region covering a plane region viewed from above including vertical interconnection for electrically connecting the interconnection layer in contact with the lower surface of the upper insulating layer and another interconnection layer in contact with the upper surface of the upper insulating layer; and an upper conductive layer selectively formed to be in contact with exposed upper surfaces of the lower insulating layer, the lower interconnection layer and the upper insulating layer in a region outside a fuse region covering a plane region including the fuse and a neighborhood thereof.
With the structure as described above, the semiconductor device can be manufactured through the manufacturing method with a reduced number of process steps as described above.
In one embodiment of the above-mentioned invention, the upper conductive layer is formed outside of the fuse region at a distance not shorter than the thickness of the coating intended to be formed on the upper conductive layer from an outline of the fuse region.
With the above-described structure, it is able to maintain the fuse region a certainly opening status even if a coating is performed on the upper conductive layer in a later step.
In the above-mentioned invention, the semiconductor device preferably comprises another insulating layer formed between the semiconductor substrate and the lower insulating layer.
With the above-described structure, a total thickness of insulating layers is tend to increase, and thus the thickness of insulating layers decreases more effectively.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.